1. Field of the Invention
The invention relates to a damper apparatus and a steering system.
2. Description of Related Art
A damper apparatus is applied to, for example, a steering system of a vehicle. The steering system changes the orientation of steered wheels of the vehicle by causing an axial reciprocating motion of a shaft connected to the steered wheels via tie rods. When the shaft is moved to an end of its movable range, end contact for physically restricting a movement of the shaft relative to a housing occurs. As described in each of Japanese Patent Application Publication No. 2012-35713 (JP 2012-35713 A) and Japanese Patent Application Publication No. 2015-128981 (JP 2015-128981 A), a damper apparatus absorbs a shock generated due to end contact, using a shock-absorbing member disposed between a shaft and a housing in the axial direction.
An elastic body having axial elasticity is used as the shock-absorbing member of the damper apparatus. The shock-absorbing member of the damper apparatus is configured such that an elastic force corresponding to a moving distance (stroke) of the shaft after occurrence of end contact is applied to the shaft. In order to restrict the movement of the shaft to a prescribed stroke or less even when an excessive axial force is input into the shaft, a spring constant of the elastic body is preferably set to be higher. However, the shock absorbing property may deteriorate as the spring constant of the elastic body is set to be higher. This causes a possibility that the shaft and an internal mechanism of the steering system will be suddenly stopped due to end contact and a high load will be applied to the internal mechanism.
In some cases, the movable range of the shaft corresponding to a maximum steered angle is set in advance so as to prevent interference between the steered wheel and a tire house cover and so forth in the steering system. However, for example, as the elastic body of the shock-absorbing member in the damper apparatus deteriorates over time, the axial position at which end contact occurs changes, and, as a result, the movable range of the shaft expands. This causes a possibility that interference between the steered wheel and the tire house cover and so forth will occur. In view of this, the damper apparatus and the steering system are required to appropriately maintain the movable range of the shaft.